Mutsumi's personality matches his expression perfectly. He's usually very calm, aside from the few times he's become flustered or angry such as when he held Serinuma's hand, when he teamed up with the other boys against Serinuma's cat-callers or when his older brother began to pursue Serinuma. He is very intelligent and has a methodical mind as seen when he realized Serinuma had been kidnapped.

Because of his quiet nature, some to most of his dialogue is overlooked in conversation and the others will carry on without his views being acknowledged in the heat of the moment. Still, he is usually the first to try to calm a heated moment and if he feels others' attitudes disturb Serinuma he immediately calls them on it and discovers a way to diffuse the tension amicably. When he was truly angered even Igarashi shuddered at his cold words, hard tone and frightening expression.

Open to any interpretation, please follow the provided clips on for the auditions.